Disc chippers are generally used in the wood processing industry for chipping wood prior to the further processing. The rotating disc of a chipper is equipped with knives attached evenly distributed thereto cutting chips from a log against a counter knife. The knives are generally attached to the disc through separate knife presses that are locked in position generally by means of a compressive force provided by bolts. The knife press by means of which the knife is pressed in its position is in this publication referred to as knife clamp.
When attaching a knife in its position in the knife disc according to a method of prior art, the knife clamp and the knife are pressed with bolts against the wear plate. The method is described e.g. in the publication U.S. Pat. No. 6,056,030. The bolts are parallel with the axis of the knife disc. The bolts have their support from the knife disc and move the knife clamp and the knife in the axial direction of the knife disc, away from the knife disc towards the inclined surface of the wear plate, against which the knife is positioned. This positioning surface of the knife in the wear plate deviates due to its inclination from the direction perpendicular to the pressing motion of the clamp, whereby the knife clamp and the knife are subject to forces from the wear plate, that tend to move the knife clamp aside from the direction of the desired pressing motion. Against this transversal motion the knife clamp is supported from the knife disc near the compressing bolt. A friction force is generated to the point of support resisting the movement of the knife clamp during the compressing process.